1. Field of the Invention
The present invention relates to an optical disc apparatus compatible with either of a mini disc (referred to as, "MD" hereinafter) and a compact disc (referred to as "CD" hereinafter) serving as data recording media for music, video, code data, and the like.
2. Description of the Prior Art
Conventionally, a CD has been popularly used as an optical disc data recording medium mainly for recording music data. In recent years, an MD has been developed as an optical disc data recording medium capable of easily recording data thereon.
The following describes MD and CD turntables of conventional MD and CD players with reference to the attached drawings.
FIGS. 8 (a), 8(b) and 8 (c) show a clamping operation of an MD turntable of a conventional MD player, while FIGS. 9 (a), 9 (b) and 9 (c) show a clamping operation of a CD turntable of a conventional CD player.
Reference is first-made to an MD turntable in connection with FIGS. 8 (a) to 8 (c), where FIGS. 8 (a) and 8 (b) show a pre-clamping condition, while FIG. 8 (c) shows a post-clamping condition. In FIGS. 8 (a) to 8 (c), an MD 100 is composed of an approximately disc-shaped transparent substrate 1 having a thickness of 1.2 mm and a magnetic thin plate 2 which is rigidly adhered to the substrate 1. The substrate 1 has its upper surface serving as a data recording surface 1a and has its lower surface serving as a ring-shaped clamp area 1b which is vertically offset by 0.8 mm, with a centering hole 1c having a diameter of 11 mm formed at the center of the substrate 1. Although the MD 100 is normally received in a cartridge, such a cartridge is not shown herein.
Reference numeral 200 denotes an MD turntable for clamping the MD 100. Reference numeral 6 denotes a rotary shaft of a spindle motor (not shown) for generating a rotational torque. Reference numeral 3 denotes a flange-shaped disc receiving section to be put in contact with the clamp area 1b when the MD 100 is clamped. Reference numeral 4 denotes a taper cone section composed of a part of a sphere, which is fitted vertically and slidably in a recess 8 formed in the disc receiving section 3. Reference numeral 7 denotes a spring member for applying a biasing force to the taper cone section 4 to be biased upward. Reference numeral 5 denotes a magnet clamper which is composed of a torus-shaped magnet 5a and a yoke 5b. The magnet clamper 5 is rigidly fixed to a portion around the center of the disc receiving section 3 in a position closer to the MD 100. The torus-shaped magnet 5a has its upper portion magnetically oriented toward the north pole. The yoke 5b is made of a magnetic substance, which surrounds the magnet 5a except for the top surface of the magnet 5a facing the MD 100.
The following describes the operation of the conventional MD turntable having the above-mentioned construction.
When the MD 100 is moved closer to the MD turntable 200 from the condition shown in FIGS. 8 (a) and 8 (b), the magnet clamper 5 attracts the magnetic thin plate 2 of the MD 100 due to its magnetic force. The substrate 1 is put in contact with the taper cone section 4 at its inner peripheral edge of the centering hole 1c. In the above place, the magnetic force of the magnet 5a further attracts the MD 100 downward, and therefore a downward force is applied to the taper cone section 4. On the other hand, since the magnet clamper 5 is rigidly fixed to the disc receiving section 3 while the taper cone section 4 is vertically slidable with respect to the disc receiving section 3, the spring member 7 which is biasing upward the taper cone section 4 is elastically compressed to depress the taper cone section 4 downward. The downward movement of the taper cone section 4 continues until the clamp area 1b is put in contact with the disc receiving section 3, and thus the MD 100 is completely clamped as shown in FIG. 8 (c).
In the condition where the disc clamping is completed, the level of the data recording surface 1a is defined by the disc receiving section 3, while the position of the MD 100 in the direction of the plane of the disc is defined by the contact of the edge of the centering hole 1c with the taper cone section 4. The height of the data recording surface 1a from the surface of the disc receiving section 3 is 0.8+1.2=2.0 mm as shown in FIG. 8 (a).
Then reference is made to the CD turntable in connection with FIGS. 9 (a) to 9 (c), where FIGS. 9 (a) and 9 (b) show a pro-clamping condition, while FIG. 9 (c) shows a post-clamping condition. In FIGS. 9 (a) to 9 (c), reference numeral 300 denotes a CD which is composed of an approximately disc-shaped transparent substrate 11 having a thickness of 1.2 mm. The substrate 11 has its top surface serving as a data recording surface 11a. In the center position of the substrate 11, there is formed a centering hole 11c having a diameter of 15 mm.
Reference numeral 400 denotes a CD turntable for clamping the CD 300. Reference numeral 16 denotes a rotary shaft of a spindle motor (not shown) for generating a rotational torque. Reference numeral 13 denotes a flange-shaped disc receiving section to be put in contact with the lower surface of the CD 300 when the CD 300 is clamped, where the disc receiving section 13 has a recess 13a and a hub-like projection 13b formed therein. Reference numeral 14 denotes a taper cone section which is composed of a part of a sphere vertically and slidably fit in the recess 13a formed in the disc receiving section 13. Reference numeral 17 denotes a spring member for applying an upward biasing force to the taper cone section 14.
Reference numeral 18 denotes a disc pressing holder having a recess 18a formed in the center portion thereof. The disc holder 18 is loaded from a CD player and moved down onto the CD 300 so as to be rotatable around the motor shaft 16 when the CD 300 is clamped on the CD turntable 400.
The following describes the clamping operation of the CD turntable having the above-mentioned construction.
When the CD 300 is moved closer to the CD turntable 400 from the condition as shown in FIGS. 9 (a) and 9 (b), the substrate 11 is engaged in contact with the taper cone section 14 at the inner peripheral edge of the centering hole 11c. In the above place, the disc pressing holder 18 is moved down onto the CD 300 to depress the CD 300 downward. Therefore, a downward force is applied to the taper cone section 14. On the other hand, since the taper cone section 14 is vertically slidable in the recess 13a of the disc receiving section 13, the spring 17 biasing upward the taper cone section 14 is elastically compressed to depress the taper cone section 14 downward. When the disc pressing holder 18 is further moved downward, the hub-like projection 13b of the disc receiving section 13 is engaged with the recess 18a of the disc pressing holder 18, thereby centering the disc pressing holder 18 with respect to the motor shaft 16. The downward movement of the taper cone section 14 due to depression of the disc pressing holder 18 is continued until the CD 300 is put in contact with the disc receiving section 13, and thus the CD 300 is completely clamped as shown in FIG. 9 (c).
In the condition where the disc clamping is completed, the level of the data recording surface 11a is defined by the disc receiving section 13, while the position of the CD 300 in the direction of the plane of the disc is defined by the engagement of the taper cone section 14 put in contact with the centering hole 11c. The height of the data recording surface 11a from the surface of the disc receiving section 13 is approximately equal to the thickness of 1.2 mm of the substrate 11.
The aforementioned constructions, however, have the following problems.
Since the MD 100 and the CD 300 are subjected to a laser beam reflection type playback operation, it is technically easy to read data of either the MD and the CD by means of an identical single optical head. When either the MD and CD can be subjected To a playback operation by means of an identical disc apparatus, a great cost reduction and the like merits can be achieved.
However, the clamping means of the MD and CD significantly differ from each other as described above, and therefore no conventional single disc drive unit can compatibly play back the discs of MD and CD. For instance, the diameter of the centering hole 1c of the MD 100 is 11 mm, whereas the centering hole 11c of the CD 300 is 15 mm. The MD 100 is clamped by utilizing the magnetic force of the magnet clamper 5, whereas the CD 300 is held by utilizing an external application force of the disc pressing holder 18. Moreover, since the MD 100 is stored in a cartridge, it is impossible to externally hold to clamp the MD 100. Furthermore, as described for the conventional example, the height of the data recording surface 1a from the disc receiving section 3 of the MD is 2.0 mm, whereas the height of the data recording surface 11a from the disc receiving section 13 of the CD is 1.2 mm.
Therefore, it has been difficult for the conventional disc apparatus or clamping means to compatibly play back either of the MD and the CD by means of an identical disc drive unit because the clamping architectures of the discs are fundamentally different from each other. Therefore, in order to provide a hybrid audio apparatus such as a radio cassette player/recorder with the capability of compatibly playing back the MD and CD, special drive units are necessary for each of the discs. The above fact results in increasing the size and weight of the apparatus as well as increasing the cost.